1. Field of the Invention
The present invention relates to a server that performs a data transfer with a client, a data transfer method, and a computer-readable recording medium.
2. Description of the Related Art
Conventionally, there have been database servers that search for data stored in a database and transfer the data as a search result to a client. Recently, to accommodate huge data, a distributed database system has been established, in which a plurality of database servers respectively having a database and a coordinator server are connected with each other via a network. In such a distributed database system, a client receives the data as the search result from the database server via the coordinator server. In the distributed database system, because the data is distributed and arranged in a plurality of databases, the coordinator server can access the database servers in parallel. Therefore, performance improvement corresponding to the number of databases can be expected. On the other hand, data transfer on the network required for transferring data between the coordinator server and the database server or between the database servers increases an overhead considerably. The same can be mentioned for a network interconnected at a high speed. Therefore, distribution effect largely decreases and the expected performance improvement may not be desired.
To deal with such a problem, a method of compressing data transferred between servers (transfer data) has been proposed. For example, Japanese Patent No. 3747525 proposes a practical method of transferring only record ID from a data server to a front end server at the time of search, and converting the record ID to an actual record in the data server at the time of fetching.
In the method of compressing the transfer data, the effect becomes large as compressibility increases. However, because in a character string with no regularity, the compressibility thereof is about 30%, and it is difficult to greatly reduce the transfer data.
Further, the method described in Japanese Patent No. 3747525 has following two problems. If a transaction in which the record is searched and a result record is sequentially updated is assumed, the effect is sufficient and responsiveness can be improved. However, in a case that a record list of a search result is instantaneously formed as in a normal full text search, a transfer amount of data increases and it is wasteful. Further, in an either-or case such that the transfer data is either record ID or actual record, it can be inconvenient. For example, it is inconvenient in a case that nonstandard data such as extensible markup language (XML) data is handled. In this case, there can be inconveniences such that data is insufficient in the former case, and useless data transfer is made in the latter case. This is because in the case of nonstandard data, the size of the data to be extracted cannot be predicted.